1. Field of the Invention
The present invention relates to an elevator and, in particular, to an apparatus for reducing vibration of an elevator car which makes it possible to reduce vibration of an elevator car for carrying passengers and freight upward and downward in a hoist in a building.
2. Description of the Background Art
FIG. 1 is an explanatory view schematically illustrating a construction of a general elevator, which includes an elevator car 1 which is directly loaded with passengers or mounted with freight and has a rubber isolator installed at a lower side, a driving device 3 which is installed at an upper side of a hoist formed in a building and generates driving force so that the car 1 is driven to be lifted in the hoist 2, a counter weight 4 which is installed at the opposite side of the car 1 and keeps the balance of the weight of the car 1, and a main rope 5 for connecting the car 1 with the counter weight 4 by the driving force generated by the driving device 3.
Herein, the main rope 5 is wound around a lifting sheave 6 installed at the driving device 3 and a pulley 7 installed at an upper side of the counter weight 4 at an interval between them and drives the car 1 in the hoist 2 by winding and unwinding the main rope 5 via the forward rotation and reverse rotation of the lifting sheave 6 by the driving force generated by the driving device 3.
Meanwhile, FIG. 2 is a cross-sectional view illustrating a connection structure of a thimble rod in the conventional art. A thimble rod 9 provided as a single body at the ends of the main rope 5 is connected to the upper portion of the car 1 and counter weight 4. A structure of the thimble rod 9 is as follows.
An insertion hole 11a is formed at the upper portion of the car 1 and counter weight 4 and at a cross head 11. The thimble rod 9 having threads formed on the outer circumferential surface thereof is inserted into thorough this insertion hole 11a.
Next, a spring 12 is installed at the inserted thimble rod 9. This spring 12 is installed at upper and lower spring seats 13a and 13b through which the thimble rod 9 passes, and fixedly connected to the car 1 and counter weight 4 by connecting a thread 10 to the outer side of the lower spring seat 13b.
The elevator thus constructed drives the driving device 3 by control of a control board (not shown) according to the operating command of an operator to thereby lifting and lowering the elevator car 1.
At this time, when the elevator car 1 is driven to be lifted and lowered, the counter weight 4 connected with the elevator car 1 by the main rope 5 is also driven to be lifted and lowered while keeping the balance of the weight of the elevator car 1.
Herein, during the car 1's traveling by the main rope 5, when the car 1 moves to an upper story, the main rope 5 at the car 1 is shortened and the main rope 5 at the counter weight 4 is lengthened, or when the car 1 moves to an lower story, the reverse is true. Since the main rope 5 is an elastic body, the rigidity thereof is decreased when the length is increased. Thus, in the case that the node of the vertical vibration mode is centered on the lifting sheave 6, when the car 1 is on an upper story, it becomes closer to the counter weight 4, or when the car 1 is on a lower story, it becomes closer to the car 1.
Subsequently, when an exciting force is transferred through the lifting sheave 6, the car 1 get in the vertical vibration mode on upper and lower stories.
However, in the conventional elevator above described, there arise problems that there is no apparatus capable of reducing only radio-frequency components according to the characteristics of the rubber isolator and dealing with vertical vibration of the entire car, although it is possible to reduce the vibration descending along the rope while passing through the rubber isolator at the lower portion of the car.
In particular, there is another problem that since a frequency of the vertical vibration mode affecting the entire car is in a low-frequency area, that is, an area sensitive to axial vibration humans feel, vertical vibration occurred during travelling of the elevator give passengers an unpleasant feeling.